Process for reducing the methane selectivity in a Fischer-Tropsch conversion of syngas to hydrocarbons, by using a catalyst composition containing (i) cobalt, either as the elemental metal, oxide, or a compound thermally decomposable to the elemental metal or oxide, (ii) zinc, in the form of the oxide or a compound thermally decomposable to the oxide, and (iii) platinum, in the elemental metal form, or in the form of a compound wherein the amount of platinum metal present in the composition is in the range 0.0001 to 1.50% w/w.